The present invention relates to a method of correcting a resonance frequency of a small rotary actuator which is used as a power means for clocks, cameras, tools, automatic assembling devices, accurate X-Y stages or the like.
Conventionally, in the case of manufacturing a small rotary actuator having a plurality of oscillators, in order to reduce a variation in a resonance frequency of the respective oscillators, there has been applied a method in which an accuracy in machining of the oscillators is improved and in which a piezoelectric element is improved through a higher accuracy process technology, or a manner in which only an excellent performing rotary actuator is selected from a plurality of rotary actuators. However, there is a limit to improving a machining accuracy, and also there arises a problem in that a yield is lowered to deteriorate productivity in the manner where only the most accurate rotary actuator is selected.
In the case where the oscillator is driven by using a piezoelectric element such as a PZT, the efficiency is the highest when the oscillator is driven with an a.c. voltage a frequency of which is identical with its resonance frequency. When the oscillator is driven with an a.c. voltage a frequency of which is different from the resonance frequency of the oscillator, a very large voltage must be applied to the oscillator, thus providing a low efficiency. When the frequency of the a.c. voltage is largely different from the resonance frequency of the oscillator, it is impossible to drive the oscillator.
In a rotary actuator of the type in which a rotary torque is produced due to continuous impact caused by the vibrations of the oscillator to drive a rotor, a large rotary torque can be obtained by providing and driving a plurality of oscillators at the same time. However, in the prior art, it is difficult to obtain an oscillator having an accurate desired resonance frequency when a small rotary actuator having a plurality of vibrators is fabricated, because the resonance frequencies are largely varied among the respective oscillators. As a result, when the oscillators are intended to be driven with an a.c. voltage a frequency of which is suitable for one oscillator, other oscillators different in resonance frequency cannot be driven, and thus the efficiency of rotation cannot be improved.
In order to reduce a variation in resonance frequency of the oscillators by improving the machining accuracy of the oscillators and the piezoelectric element, the manufactured devices and the manufacturing processes need to be improved, and the costs cannot be prevented from largely increasing. As a result, it is difficult to manufacture a highly efficient actuator.